I would argue that there is no such thing as "the business model". There may be a projected rolled up summary state... but that's only one possible view out of infinitely many. For example, one possible "business model" could be "customers who have changed their emails in the past month". You shouldn't favor any particular view as being the favored "business model"... unless you're doing snapshots, in which case everything goes out the window.

Basically, I vote for `SetCustomerEmail`.